This invention relates to plate heat exchangers and plate evaporators, hereinafter referred to collectively as plate heat transfer apparatus.
In such heat transfer apparatus, heat is transferred between two thin, broad streams, which may be both of liquid or one stream of liquid and one stream of vapour or two streams of vapour. In some cases one or both streams may have mixed liquid and vapour phases. The streams are separated by plates assembled in a spaced face-to-face relationship to provide flow spaces between the adjacent faces of the plates. The boundaries of the flow spaces are enclosed and sealed by flexible or resilient gaskets surrounding the flow spaces between the adjacent faces, and disposed between the flow spaces and entry and exit ports. The ports, in plate heat exchangers usually one at each corner of the plate, are similarly surrounded or part-surrounded by gaskets as appropriate to control the flow to and from the flow spaces.
Each gasket is normally of a one piece construction set within a pressed recess formed in the plate. The manufacture of the gasket is normally carried out in moulds, but according to the size of the plate of the manufacturing techniques used, the gasket may be assembled from two or more smaller components. The gaskets are normally moulded of an elastomeric material.
The sealing force against the fluid pressure in the flow space is obtained by compression of the gaskets in a direction normal to the plate surface.
A conventional generally rectangular heat transfer plate with a port near each corner is normally regarded as having a main heat transfer zone covering a majority of the area of the plate. At each end, the plate has a distribution region, which is part of the heat transfer zone, over which the feed fluid is distributed from the port over the width of the plate, or is collected from the width of the plate and directed towards the port. In view of the different functions of the different areas of the plate, the arrangement of corrugations or other formations on them may be markedly different.
One port, a transfer port, at each end of the plate is isolated from the flow space by a length of gasketing surrounding the port, the port gasket. The other port at each end, the flow port, will be in communication with the heat transfer zone. Between each port and the distribution region is an area, the bridge zone, and normally the transfer bridge zones associated with the transfer ports are also isolated from the flow space by lengths of gasket, bridge gaskets. The transfer bridge zones are thus doubly isolated and normally can be used as vented leakage spaces. Depending on the orientation of the vents from the transfer bridge zones and the shape of the adjacent gasketing, it is possible that vented fluids can accumulate in dead spaces between the plates and not easily or naturally drain or move out of the dead spaces and away from the apparatus especially if the vents become blocked with debris or crystalline deposits.